The optical switch of the present invention comprises Risley prisms (i.e., pairs of wedge prisms) to redirect light beams from an array of input ports to an array of output ports. The invention further comprises a stepping rotary microactuator for independent rotation of each wedge prism of a Risley prism pair to redirect the light beams.
As the demand for network capacity grows, telecommunications are being increasingly constrained by the need for more bandwidth. Optical fiber is a transmission medium capable of meeting this demand, having the potential in combination with dense wavelength division multiplexing (DWDM) to provide carrying capacity in a single fiber of hundreds of trillions of bits (terabits) per second, far greater than other means suggested for long-distance communications.
However, network transmission speeds and equipment costs are currently severely limited by the requirement of slow and complex electronic switching for signal routing—converting an optical (i.e., photonic) signal from an input optical fiber into an electronic signal, switching the lower speed electronic signal, converting the electronic signal back to an optical signal, and redirecting the optical signal through an output optical fiber. In particular, it is unlikely that such optoelectronic switching will be able to accommodate the large increase in network bandwidth that will accompany the full implementation of DWDM. To fully exploit an optical fiber's full bandwidth will likely require integrating the transmission, combination, amplification, and switching of optical signals in an all-optical network without optoelectronic switching. Furthermore, efficient switching of terabit optical signals from an input optical fiber array to an array of output optical fibers may require optical cross-connect switches with 256-input×256-output ports or more.
A number of technologies have been proposed to provide an all-optical switch for telecommunications. These include micromachined tilting mirrors, liquid crystals, bubbles, holograms, and thermo- and acousto-optics. However, none of these technologies are likely to satisfy a wide range of applications, as the requirements for optical fiber array size, scalability, switching speed, reliability, optical loss, cost, and power consumption differ greatly depending on the functionality desired.
In particular, microelectromechanical systems (MEMS) technology has been proposed for optical cross-connects whereby arrays of micromirrors are built on a silicon wafer using surface micromachining fabrication similar to that used in making integrated circuits. These MEMS optical switches use micromirrors to redirect light beams from as many as 256-input to 256-output ports. Each micromirror can be less than 1 millimeter in diameter. However, such a MEMS switch is complex. Furthermore, switching times can be slow and the long-term reliability of moveable parts is a concern. Additionally, the spatial resolution of the MEMS switch may need improvement for some applications. In a large cross-connect switch, the mirrors must be capable of a large range of angular motion, yet be able to accurately move an incident light beam through small tilt angles in order to redirect the incident light beam to a particular output optical fiber and achieve low optical throughput loss. Finally, this MEMS switch requires tightly controlled cleanroom fabrication and contaminant-free switch operation.
Particularly for cross-connect applications, there remains a need for a reliable, scalable, low loss, fast, and low cost optical switch.